// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef BASE_WIN_SCOPED_COM_INITIALIZER_H_
#define BASE_WIN_SCOPED_COM_INITIALIZER_H_

#include <objbase.h>

#include "base/logging.h"
#include "base/macros.h"
#include "build/build_config.h"

namespace base {
namespace win {

    // Initializes COM in the constructor (STA or MTA), and uninitializes COM in the
    // destructor.
    //
    // WARNING: This should only be used once per thread, ideally scoped to a
    // similar lifetime as the thread itself.  You should not be using this in
    // random utility functions that make COM calls -- instead ensure these
    // functions are running on a COM-supporting thread!
    class ScopedCOMInitializer {
    public:
        // Enum value provided to initialize the thread as an MTA instead of STA.
        enum SelectMTA { kMTA };

        // Constructor for STA initialization.
        ScopedCOMInitializer()
        {
            Initialize(COINIT_APARTMENTTHREADED);
        }

        // Constructor for MTA initialization.
        explicit ScopedCOMInitializer(SelectMTA mta)
        {
            Initialize(COINIT_MULTITHREADED);
        }

        ~ScopedCOMInitializer()
        {
#ifndef NDEBUG
            // Using the windows API directly to avoid dependency on platform_thread.
            DCHECK_EQ(GetCurrentThreadId(), thread_id_);
#endif
            if (succeeded())
                CoUninitialize();
        }

        bool succeeded() const { return SUCCEEDED(hr_); }

    private:
        void Initialize(COINIT init)
        {
#ifndef NDEBUG
            thread_id_ = GetCurrentThreadId();
#endif
            hr_ = CoInitializeEx(NULL, init);
#ifndef NDEBUG
            if (hr_ == S_FALSE)
                LOG(ERROR) << "Multiple CoInitialize() calls for thread " << thread_id_;
            else
                DCHECK_NE(RPC_E_CHANGED_MODE, hr_) << "Invalid COM thread model change";
#endif
        }

        HRESULT hr_;
#ifndef NDEBUG
        // In debug builds we use this variable to catch a potential bug where a
        // ScopedCOMInitializer instance is deleted on a different thread than it
        // was initially created on.  If that ever happens it can have bad
        // consequences and the cause can be tricky to track down.
        DWORD thread_id_;
#endif

        DISALLOW_COPY_AND_ASSIGN(ScopedCOMInitializer);
    };

} // namespace win
} // namespace base

#endif // BASE_WIN_SCOPED_COM_INITIALIZER_H_
